Lactic acid, CH3CH(OH)COOH\text{CH}_3\text{CH(OH)COOH}CH3CH(OH)COOH (pKa=3.86\text{p}K_a = 3.86pKa=3.86), is a weak monobasic acid found in sour milk products and produced in muscles during intense exercise. A buffer solution is prepared by adding 70.0 cm370.0\text{ cm}^370.0 cm3 of 0.600 mol dm−30.600\text{ mol dm}^{-3}0.600 mol dm−3 lactic acid to 30.0 cm330.0\text{ cm}^330.0 cm3 of 0.800 mol dm−30.800\text{ mol dm}^{-3}0.800 mol dm−3 sodium hydroxide, NaOH\text{NaOH}NaOH.
Explain why a buffer solution is formed.
Calculate the pH of the buffer solution that has been prepared. Give your answer to 2 decimal places.
A small amount of aqueous ammonia, NH3(aq)\text{NH}_3(\text{aq})NH3(aq), is added to the buffer solution. Explain, in terms of equilibrium, how the buffer solution would respond to the added NH3(aq)\text{NH}_3(\text{aq})NH3(aq).
